The embodiments of the present invention relate generally to systems for removing and controlling solids suspended in a liquid slurry. More particularly, the embodiments provide a mobile system for storing and processing drilling fluids.
Rigs used for drilling hydrocarbon wells are large, complex assemblies of machinery. While drilling rigs used offshore are often integrated into a single platform, almost all rigs used to drill wells on land are designed to be disassembled, transported between drilling sites, and reassembled. Although some rigs may be designed to be moved by helicopter or airplane, the majority of rigs are moved by trucks and trailers. Thus, many land rigs are designed to disassemble into components sized so as to be quickly and easily loaded onto, transported by, and offloaded from a trailer.
The process of assembling a land rig for drilling operations is known as “rig up.” During rig up, all of the various components of the drilling rig are assembled and tested prior to any drilling activity taking place. The rig up procedure may last anywhere from a couple of days to more than a week, depending on the type of rig being assembled and any problems encountered during the process. Because drilling the well can not commence until rig up is complete, it is desirable to minimize the time spent assembling the drilling rig.
The entire rig up process must be performed in reverse order to “rig down,” the process used to disassemble the rig for transportation to another location. During rig down, the individual rig components are disconnected and loaded, by cranes or winches, onto trailers for transport. The rig down procedures further add to the downtime that the rig spends between drilling wells, and are therefore conducted as quickly as safety permits.
The amount of downtime spent between drilling wells is often limited by the contract under which the rig is operating. These contracts often specify the time permitted for rig up and rig down, and that any time beyond the permitted limits will not be paid for by the rig lessee, but will be paid for by the rig operator. Thus, any equipment or procedures that may be available to lessen the amount of time needed for rig up and rig down activities are desirable and would be welcomed by the industry.
One key component of a drilling rig is the drilling fluid circulation system or mud system, which circulates drilling fluid (mud) through the wellbore. The circulation system is also used to maintain the density of the drilling fluid by removing drilled cuttings from the fluid, and adding other solids to the fluid as may be desired. The density of the drilling fluid is critical to hole cleaning, rate of penetration, and pressure control in the well. Hole cleaning and rate of penetration are important factors in the efficiency of the drilling process, while pressure control is critical to safely drilling a well.
In general operation, drilling fluid is pumped by high-pressure mud pumps through the drill string and into the wellbore. The fluid exits the drill string at the bit and returns to the surface through the annulus between the drill string and the wellbore, carrying cuttings from the hole to the surface. The hydrostatic pressure from the column of drilling fluid prevents fluids from the surrounding formation from entering the wellbore and potentially causing a loss of well control.
At the surface, the drilling fluid is then processed, in order to maintain the desired density, before it is pumped back through the drill string into the hole. Solids control equipment such as shakers, degassers, desilters, desanders, and centrifuges may be used to process the drilling fluid at the surface by removing solids and entrained gases from the fluid. The density of the drilling fluid may be increased by adding a higher density fluid or select solid materials to the fluid. The drilling fluid, including a reserve volume is typically stored in tanks or pits at the surface before being recirculated through the well.
For land-based, mobile drilling rigs, the circulation system is often subdivided into skid-mounted modules that can be easily transported by truck between well sites. These skid-mounted modules are normally designed to be lifted by cranes onto trailers or pulled onto flatbed trailers by winches. Common modules include mud tanks, solids control equipment, jetting equipment, and a gravity fed manifold. A common circulation system may include more than one module of each type, but every module employed in the system increases the time needed for rig up and rig down operations.
The mud tank modules provide a reservoir of drilling fluid for use during circulation. Most conventional mud tank modules include open top, rectangular tanks, but round tanks are also occasionally used. At one end of the typical mud tank module is a “porch” for mounting pumps and other equipment that is used to move fluid into and out of the tanks. The mud tanks also preferably have access hatches or manways through the sides of the tanks designed to provide access into the tank to facilitate cleaning, since solids tend to accumulate in the tanks. The tanks are usually cleaned periodically during operations, and also between well drilling operations. The mud tanks may also have agitators or stirrers provided to keep the fluid circulating within a single tank in order to minimize settling of the solids.
An assortment of other modules are also used in conjunction with the mud tanks and are thus in fluid communication with the tanks. The solids control module includes the shakers, desilters, desanders, mudcleaners, agitators, mud hoppers, centrifuges, degassers, etc. and may include one or more skids, to which the equipment is mounted. Jetting equipment is used to supply high pressure fluid to clean or remove deposits from the inside of the mud tanks. Jetting equipment may also be used in conjunction with a tanker truck or vacuum truck to clean out the mud tanks and remove unwanted fluids. The gravity fed manifold is used to control and route the supply of drilling fluid from the mud tanks to the triplex pumps, which are used to circulate the drilling mud down the wellbore and throughout the system. The jetting equipment, and manifold all require one or more skids each.
With all of the different equipment that has to be integrated into a typical fluid circulation system, it can be seen that the effort required to transport and assembly such a system is considerable. Thus, there remains a need in the art for systems that decrease the time needed for rig up and rig down of a fluid circulation system. Therefore, the embodiments of the present invention are directed to methods and apparatus for providing a mobile fluid circulation system that seeks to overcome certain of the limitations of the prior art.